Baseband echo rapid generation method based on frequency domain target scattering characteristics

Abstract

The invention belongs to the technical field of echo generation, and particularly relates to a baseband echo rapid generation method based on frequency domain target scattering characteristics. According to the scheme, after radio frequency target scattering characteristics are down-converted to a base band, frequency domain processing is carried out on the frequency spectrum of a transmitted signal and the target scattering characteristics in a base band domain, so that the sampling rate requirement is greatly reduced, the calculated amount is reduced, and meanwhile the simulation precision equivalent to that of traditional radio frequency echoes is kept. Compared with a traditional time-domain echo generation method, the non-linear scattering behavior of the target in any attitude can be accurately simulated by introducing the target radio frequency domain scattering characteristics obtained based on an electromagnetic simulation tool, so that the authenticity of echo signals is remarkably improved. Meanwhile, compared with high calculation overhead of radio frequency domain simulation under several GHz sampling, equivalent frequency domain calculation is completed under the baseband sampling rate, so that the echo generation speed is increased by dozens of times compared with the radio frequency domain simulation, and the generation speed of target echoes is increased.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of echo generation, and particularly relates to a baseband echo fast generation method based on frequency domain target scattering characteristics. BACKGROUND

[0002] Radar echo simulation is an important part of radar system development and radar signal processing technology research, and is crucial for algorithm verification and radar system parameter optimization. Common target echo simulation methods mainly include two categories: time domain echo simulation and frequency domain echo simulation. The time domain method mainly includes point target simulation based on target scattering statistical model (such as Swerling model) and extended target simulation based on target scattering center model. However, these two types of time domain methods generally have the problem of insufficient precision: the statistical model method can only simulate the average scattering characteristics and lacks specificity for specific targets; and the scattering center method needs to pre-fit the scattering center parameters of the target, making it difficult to flexibly and efficiently simulate the real echo characteristics of the target in any attitude. Therefore, the current research and application of high-precision and real echo simulation of targets in any attitude mainly rely on frequency domain simulation methods, but the traditional radio frequency frequency domain echo simulation method mainly has the following problems:

[0003] (1) The sampling rate of the traditional radio frequency echo simulation is linearly related to the carrier frequency: according to the Nyquist sampling theorem, the traditional radio frequency echo simulation must digitize the transmitted signal and the echo signal at a sampling rate not lower than twice the carrier frequency. With the increase of radar carrier frequency from several GHz to tens of GHz, the required sampling rate must also be linearly increased, resulting in a significant increase in data storage and data preprocessing computation with the increase of carrier frequency.

[0004] (2) Large amount of calculation and slow simulation speed: with the increase of radar carrier frequency, the spectrum of the traditional radio frequency echo simulation method is usually stored and operated at a high sampling rate of GHz, which greatly increases the calculation amount of subsequent frequency domain point multiplication and inverse transform, making it difficult to meet the simulation needs of real-time or large-scale target library.

[0005] In view of the above problems, in order to balance the simulation accuracy and calculation efficiency, the application proposes a baseband echo fast generation method. This method down-converts the radio frequency target scattering characteristics to baseband, and then processes the frequency spectrum of the transmitted signal and the target scattering characteristics in the baseband domain, which not only maintains the scattering accuracy comparable to radio frequency simulation, but also reduces the sampling rate from GHz to MHz, greatly reducing the data amount and calculation amount, and achieving a tens-of-times improvement in echo generation speed. SUMMARY

[0006] The technical scheme adopted by the application is:

[0007] A baseband echo fast generation method based on frequency domain target scattering characteristics, considering the "walk-stop-walk" model, setting the radial distance between the radar and the geometric center of the target as , the baseband signal transmitted by the radar as , the radio frequency time domain response of the target as , the baseband time domain response of the target obtained by down conversion as , the baseband echo received by the radar as , the baseband echo can be expressed as:

[0008]

[0009] wherein, is the propagation delay of the baseband transmitted signal, and the frequency domain formula corresponding to the above formula is:

[0010]

[0011] wherein, is the spectrum of the baseband echo, is the spectrum of the baseband transmitted signal, is the baseband frequency domain response of the target after down conversion, is the phase factor caused by the distance.

[0012] In the formula, is the imaginary unit, defined as: ; is the angular frequency of the radar, defined as , wherein is the working frequency of the radar; is the radial distance between the radar and the geometric center of the target; is the speed of light, generally taken as

[0013] Therefore, the baseband echo fast generation method comprises the following steps:

[0014] S1, calculating the spectrum of the baseband transmitted signal: performing Fourier transform on the baseband time domain signal transmitted by the radar to obtain the spectrum :

[0015]

[0016] wherein, represents Fourier transform.

[0017] S2, obtaining the baseband frequency domain scattering characteristics of the target: modeling the target and calculating the target characteristics by using an electromagnetic simulation calculation software (such as FEKO) to obtain the frequency domain scattering characteristics of the target at the working radio frequency of the radar , and perform down-conversion operation to obtain the baseband frequency domain scattering characteristics of the target :

[0018]

[0019] S3, frequency domain interpolation: frequency domain scattering characteristics of target baseband Perform frequency domain interpolation to make the number of sampling points and the transmitted baseband signal spectrum The number of sampling points is consistent, and the interpolation algorithm can use high-precision cubic spline interpolation to ensure and Match at the same discrete frequency points.

[0020] S4. Frequency domain dot product and range phase modulation: The frequency domain representation of the target echo is as follows:

[0021]

[0022] The spectrum of the transmitted baseband signal And the target baseband frequency domain scattering characteristics after interpolation Perform point-by-point multiplication and then calculate the radial distance between the radar and the target geometric center. Adding distance-induced phase modulation , the spectrum of the baseband echo signal can be obtained .

[0023] S5, time-frequency domain conversion and range gate movement: the baseband echo signal spectrum obtained in S4 Perform inverse Fourier transform to get the echo :

[0024]

[0025] in, represents the inverse Fourier transform.

[0026] According to the radial distance between the radar and the target geometric center Calculate the delay of the baseband transmission signal , then the corresponding range gate index for:

[0027]

[0028] in, is the time domain sampling rate of the echo signal.

[0029] The number of points within the effective pulse width is :

[0030]

[0031] in, is the pulse width of the radar baseband transmit signal.

[0032] Will The front Move the point to the range gate index The final target baseband echo signal is obtained .

[0033] The beneficial effects of the present invention are as follows: compared with the traditional time-domain echo generation method, the present invention can accurately simulate the nonlinear scattering behavior of the target in any posture by introducing the target radio frequency frequency domain scattering characteristics obtained based on electromagnetic simulation tools, thereby significantly improving the authenticity of the echo signal. At the same time, compared with the high computational overhead of radio frequency frequency domain simulation under several GHz sampling, the present invention completes the equivalent frequency domain calculation at the baseband sampling rate, thereby achieving an echo generation speed that is dozens of times higher than that of radio frequency frequency domain simulation, thereby accelerating the generation speed of the target echo. Overall, the present invention is implemented by optimizing the calculation process and algorithm, and while taking into account the accuracy of echo generation, it improves the generation speed of the target baseband echo, and can better adapt to the needs of large-scale, multi-target echo simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Generate an algorithm flow chart for traditional RF echo;

[0035] Figure 2 This is a flow chart of the baseband echo rapid generation algorithm proposed by the present invention;

[0036] Figure 3 It is the IQ diagram of the baseband echo of the ship target;

[0037] Figure 4 Comparison of pulse compression results for ship target echoes;

[0038] Figure 5 This is a comparison chart of the simulated speeds of traditional RF echo and baseband echo of the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0040] The application provides a baseband echo fast generation method based on frequency domain target scattering characteristics. The method downconverts high-resolution radio frequency scattering characteristic data obtained by electromagnetic calculation software to a baseband, and interpolates and resamples the baseband scattering characteristic data to the same frequency sampling axis as a baseband spectrum of a transmission signal. Then, the baseband spectrum of the transmission signal and the baseband scattering spectrum of the target are multiplied point by point in the baseband domain, the round trip time delay of the target is calculated according to a "stop-and-go" motion model, and the echo spectrum is modulated by applying a phase factor in the frequency domain. Finally, the time domain signal is restored by performing fast inverse Fourier transform on the modulated frequency domain echo, and the sampling sequence corresponding to the effective pulse width is moved to the correct range gate position according to the calculated time delay, so that the baseband time domain echo of the target is finally obtained.

[0041] Embodiment

[0042] This embodiment uses a Matlab simulation platform for experiments.

[0043] The method of the embodiment is shown in the attached Figure 2 figure.

[0044] The radar transmission waveform is a linear frequency modulation wave, and the echo simulation model uses a "stop-and-go" model, without considering the amplitude modulation caused by the radar equation.

[0045] The target type is a ship target, and the target scattering characteristic calculation conditions are: radar operating frequency , bandwidth , sweep interval . According to the target scattering characteristic calculation conditions, the target observation size , and the radar range resolution are obtained.

[0046] Step one: data loading and simulation parameter setting: load the target radio frequency scattering characteristic data, set the radar waveform as a linear frequency modulation wave, set the radar transmission signal parameters: radar operating frequency , bandwidth , sampling rate , pulse width , pulse repetition period , set the radial distance between the radar and the geometric center of the target , and the speed of light ;

[0047] Step two: generate a baseband transmission signal according to the set radar transmission signal parameters , then perform point fast Fourier transform on the baseband transmission signal to obtain its frequency spectrum , that is, calculate:

[0048]

[0049] in, for The discretization representation of for The discretization representation of represents the fast Fourier transform, Get the time domain length of the transmitted baseband signal:

[0050]

[0051] The length of the baseband signal transmitted in this embodiment ;

[0052] Step 3: Load the target RF frequency domain scattering data Downconversion to baseband ,Right now:

[0053]

[0054] in Then, the baseband scattering characteristic data is interpolated by cubic spline and resampled to make the number of points equal to The points are the same.

[0055] This embodiment Number of origin points , need to be resampled to ;

[0056] Step 4: Baseband target frequency domain characteristics and the transmitted signal baseband spectrum Perform frequency domain processing and calculate the spectrum of the target baseband echo according to the following formula:

[0057]

[0058] in is the phase modulation factor, , ,but

[0059]

[0060] Step 5: Perform fast inverse Fourier transform to obtain , that is, calculate:

[0061]

[0062] in, for The discretization representation of for The discretization representation of stands for fast inverse Fourier transform.

[0063] The number of points within the effective pulse width is calculated according to the following formula :

[0064]

[0065] The number of points within the effective pulse width of the present embodiment ;

[0066] The distance gate index is calculated according to the following formula:

[0067]

[0068] The time delay of the present embodiment , the distance gate index ;

[0069] The first points in are moved to the distance gate index , and the target baseband echo as shown in the attached Figure 2 is obtained, wherein the real part of the echo is , and the imaginary part of the echo is .

[0070] Step six: the pulse compression operation shown in the following formula is performed on the obtained , and the pulse compression figure thereof is obtained:

[0071]

[0072] wherein, is the pulse compression result, is the reference signal, and the present embodiment can take , represents the complex conjugate of .

[0073] It is observed whether the distance gate is the same as the radial distance set between the radar and the geometric center of the target , and is compared with the time domain response of the target scattering characteristic data and the pulse compression figure of the echo generated by the conventional radio frequency method. Figure 1

[0074] Step seven: the radio frequency domain data of the radar working frequency , bandwidth , and sweep interval are loaded, and the conventional radio frequency echo generation algorithm shown in the attached Figure 1 and the attached Figure 2 ​​​The baseband frequency domain fast generation algorithm of the application is shown. 100 simulations are independently performed under the same input data and parameter configuration, and the total calculation time of each simulation is recorded and averaged to compare the calculation efficiency of the application and the traditional radio frequency end simulation method.

[0075] Appendix Figure 3 The simulation output of the baseband echo fast generation algorithm in this embodiment is shown in the appendix Figure 4 The comparison results of the output after pulse compression processing with the ship target electromagnetic simulation time domain response and the traditional radio frequency echo pulse compression. It can be observed that the distance gate in the pulse compression figure is consistent with the radial distance between the set radar and the geometric center of the target And the peak relative amplitude, peak distribution are consistent with the ship time domain echo response obtained by electromagnetic simulation and the traditional radio frequency echo pulse compression result, which proves that the simulation accuracy of the baseband echo of the application is consistent with the traditional radio frequency echo.

[0076] Appendix Figure 5 The average time comparison chart of the traditional radio frequency echo and the baseband echo simulation speed of the application, which shows the average time comparison of the traditional radio frequency echo generation method and the baseband frequency domain fast generation method of the application. With the carrier frequency increasing from 1GHz to 10GHz, the echo generation time of the traditional radio frequency simulation method increases linearly: from about 12ms to nearly 68ms; while the baseband echo fast generation algorithm proposed in the application has a sampling rate only related to the baseband bandwidth , so the baseband echo generation time is stable at about 2.5ms.

[0077] Appendix Figure 4 and appendix Figure 5 The baseband echo fast generation method based on the target frequency domain scattering characteristics proposed in the application not only accurately generates the target echo according to the target scattering characteristics, but also realizes tens of times acceleration in speed compared with the traditional radio frequency echo generation method, which can better adapt to the large-scale, multi-target echo simulation demand.​

Claims

1. A method for rapid generation of baseband echo based on frequency domain target scattering characteristics, setting the radial distance between the radar and the target geometric center to , the baseband signal transmitted by the radar is , the target's RF time domain response is , the target baseband time domain response obtained by down-conversion is , the baseband echo received by the radar is , baseband echo Expressed as: ， in, is the propagation delay of the baseband transmission signal, The corresponding frequency domain formula is: ， in, is the spectrum of the baseband echo, is the spectrum of the baseband transmitted signal, is the baseband frequency domain response after target down-conversion, is the phase factor caused by distance, is the imaginary unit, defined as: ; is the radar operating angular frequency, defined as ,in is the radar operating frequency; is the radial distance between the radar and the geometric center of the target; is the speed of light; It is characterized in that the baseband echo rapid generation method comprises the following steps: S1. Calculate the spectrum of the baseband transmission signal: the baseband time domain signal transmitted by the radar Perform Fourier transform to obtain its spectrum : ， in, represents Fourier transform; S2. Obtain the target baseband frequency domain scattering characteristics: Use electromagnetic simulation software to model the target and calculate the target characteristics to obtain the target's frequency domain scattering characteristics at the radar operating RF frequency. , perform down-conversion operation to obtain the baseband frequency domain scattering characteristics of the target : ， S3, frequency domain interpolation: frequency domain scattering characteristics of target baseband Perform frequency domain interpolation to make the number of sampling points and the transmitted baseband signal spectrum The number of sampling points is consistent, and the interpolation algorithm uses high-precision cubic spline interpolation to ensure and Match at the same discrete frequency points; S4. Frequency domain dot product and range phase modulation: The frequency domain representation of the target echo is as follows: ， The spectrum of the transmitted baseband signal And the target baseband frequency domain scattering characteristics after interpolation Perform point-by-point multiplication and then calculate the radial distance between the radar and the target geometric center. Adding distance-induced phase modulation , get the spectrum of the baseband echo signal ; S5, time-frequency domain conversion and range gate movement: the baseband echo signal spectrum obtained in S4 Perform inverse Fourier transform to get the echo : ， in, represents the inverse Fourier transform; According to the radial distance between the radar and the target geometric center Calculate the delay of the baseband transmission signal , then the corresponding range gate index for: ， in, is the time domain sampling rate of the echo signal; The number of points within the effective pulse width is : ， in, is the pulse width of the radar baseband transmission signal; Will The front Move the point to the range gate index The final target baseband echo signal is obtained .

Images